The present invention relates to a method for removing layers of hard material, except TiN, from hard metal substrates.
Definition
For the purpose of this disclosure, xe2x80x9chard material layerxe2x80x9d means a layer comprising an oxide, nitride, carbide, carbonitride or carboxynitride of at least one element of groups 4, 5, 6, 13, 14 according to the xe2x80x9cNew IUPAC Notationxe2x80x9d, for example according to the xe2x80x9cCRC Handbook of Chemistry and Physicsxe2x80x9d, CRC Press, 77th Edition, xe2x80x9cPeriodic Table of Elementsxe2x80x9d, wherein the hard material layers comprising the above listed materials are poorly soluble in solutions comprising H2O2. TiN is excluded from these hard materials.
German Patent DE 43 39 502 discloses removing, as hard material layers, duplex layers comprising TiN/TiAlN from hard metal substrates by means of complexly composed solutions based on hydrogen peroxide.
The solution applied according to DE 43 39 502 for the layer removal of TiN/TiAlN duplex hard material layers satisfies the requirements for short layer removal times and for the capacity for being carried out only slightly above ambient temperature. But, due to its complex composition, it does not satisfy the requirement for simple [waste] disposal. In addition, the solutions used, which indiscriminately dissolve the TiN and TiAlN layers, lead to an unacceptable degradation of the hard metal substrate surface. The solutions employed are expensive.
It is the task of the present invention to remedy the above disadvantages and to propose a layer removal method for hard material layers which, on the one hand, retains the advantages of the method known from DE 43 39 502, namely with respect to short layer removal times and layer removal temperature, but, in addition, degrades the hard metal substrate surface far less, is simple in the solution composition and can be readily disposed.
This is attained according to the invention by applying, between the substrate and the hard material layer, a TiN intermediate carrier layer and wherein the hard material layer is removed by selectively dissolving predominantly only the TiN layer, namely through pores of the hard material layer. This also explains why the method according to the invention is not intended for TiN hard material layers themselves, even if this method can be employed quite reasonably in order to remove layers from workpieces with hard material layers of the above type and simultaneously, or basically in the same bath, remove layers from TiN-coated workpieces.
According to the invention it was found that, if the intent is not directed toward the purpose of dissolving the hard material layer itself but toward providing between hard metal substrate and hard material layer an intermediate carrier layer, which can be dissolved substantially more simply than the hard material layer per se, because of the porosity which is always present, in particular, in PVD-applied hard material layers, leads to the undermining of this layer and the dissolving of the intermediate carrier layer. This leads to the fact that the hard material layer, which is not at all, or substantially less, dissolved, falls off.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying descriptive matter in which a preferred embodiment of the invention is illustrated.
In a preferred embodiment of the method, hard material layers are removed which comprise a layer of type
(E1, E2 . . . En)X
wherein
Ex: is an element No. n=x from one of the groups 4, 5, 6, 13, 14 according to the New IUPAC Notation of the Periodic Table of Elements, where
X: is at least one element of the group containing N, C, O; and
n: is a running parameter, with nxe2x89xa72, in particular with n=2.
The thickness of the intermediate layer is substantially less than that of the functional hard material layer. The intermediate layer thickness dz is preferably selected as follows:
0.01 xcexcmxe2x89xa6dzxe2x89xa60.5 xcexcm,
preferably
0.01 xcexcmxe2x89xa6dzxe2x89xa60.3 xcexcm,
especially preferred
0.01 xcexcmxe2x89xa6dzxe2x89xa60.2 xcexcm.
In a further preferred embodiment of the method according to the invention the elements Exxe2x80x94with 1xe2x89xa6xxe2x89xa6nxe2x80x94comprise Al and/or Si and/or Cr and/or boron. In a further preferred embodiment of the method according to the invention the hard material layer comprises a CrC, CrN, CrCN or a WCxe2x80x94C layer.
In a further preferred embodiment of the method according to the invention the hard material layer comprises a TiAlN and/or TiCrN layer, wherein in an especially preferred embodiment the hard material layer comprises a TiAlN layer, therein, in particular preferred, is a TiAlN layer.
The hard material layer preferably has a layer thickness of at least 2 xcexcm.
As the solution is preferably used a hydrogen peroxide solution, therein preferably with maximally 50 wt. % hydrogen peroxide, in particular preferred with maximally 20 wt. % hydrogen peroxide. To this solution further is preferably added NaOH, this preferably at maximally 5 wt. % in particular preferred maximally 0.5 wt. %.
Further, to the solution is therein preferably added at least one of the substances disodium oxalate, KNa tartrate tetrahydrate, preferably maximally 5 wt. %, in particular preferred maximally 0.5 wt. %. In an especially preferred embodiment, the solution employed comprises, in addition to water, exclusively hydrogen peroxide, preferably at the stated percentages by weight, as well as NaOH, also preferred at the stated percentages by weight, as well as at least one of the listed substances disodium oxalate, KNa tartrate tetrahydrate, also preferably in the stated concentration.